1. Field of the Invention
The present invention relates to a method of treating a glutamate abnormality and a method of effecting a neuronal activity in an animal using a NAALADase inhibitor, and a pharmaceutical composition comprising an effective amount of a NAALADase inhibitor for treating a glutamate abnormality and effecting a neuronal activity in an animal.
2. Description of the Prior Art
Glutamate Abnormalities
Glutamate has been implicated in various neurological diseases and conditions, including epilepsy, stroke, Alzheimer""s disease, Parkinson""s Disease, Amyotrophic Lateral Sclerosis (ALS), Huntington""s Disease, schizophrenia, chronic pain, ischemia and neuronal loss following hypoxia, hypoglycemia, ischemia, trauma and nervous insult. Neurons release glutamate in great quantities when they are deprived of oxygen, as may occur during an ischemic brain insult such as a stroke or a heart attack. This excess release of glutamate in turn causes over-stimulation (excitotoxicity) of NMDA, AMPA, Kainate and MGR receptors. When glutamate binds to these receptors, ion channels in the cell membranes of the neurons open, permitting flows of ions across the cell membranes, e.g., Ca2+ and Na+ into the cells and K+ out of the cells. These flows of ions, especially the influx of Ca2+, cause over-stimulation of the neurons. The over-stimulated neurons secrete more glutamate, creating a domino-effect which ultimately results in cell death via the production of proteases, lipases and free radicals.
Attempts to prevent excitotoxicity by blocking NMDA, AMPA, Kainate and MGR receptors have proven difficult because each receptor has multiple sites to which glutamate may bind. Many of the compositions that are effective in blocking the receptor are also toxic to animals. As such, there is currently no known effective treatment for glutate abnormalities.
NAALADase Inhibitors
NAAG and NAALADase have been implicated in several human and animal pathological conditions. For example, it has been demonstrated that intra-hippocampal injections of NAAG elicit prolonged seizure activity. More recently, it was reported that rats genetically prone to epileptic seizures have a persistent increase in their basal level of NAALADase activity. These observations support the hypothesis that increased availability of synaptic glutamate elevates seizure susceptibility, and suggest that NAALADase inhibitors may provide anti-epileptic activity.
NAAG and NAALADase have also been implicated in the pathogenesis of ALS and in the pathologically similar animal disease called Hereditary Canine Spinal Muscular Atrophy (HCSMA). It has been shown that concentrations of NAAG and its metabolitesxe2x80x94NAA, glutamate and aspartatexe2x80x94are elevated two- to three-fold in the cerebrospinal fluid of ALS patients and HCSMA dogs. Additionally, NAALADase activity is significantly increased (two- to three-fold) in post-mortem spinal cord tissue from ALS patients and HCSMA dogs. As such, NAALADase inhibitors may be clinically useful in curbing the processing of ALS if increased metabolism of NAAG is responsible for the alterations of CSF levels of these acidic amino acids and peptides.
Abnormalities in NAAG levels and NAALADase activity have also been documented in post-mortem schizophrenic brain, specifically in the prefrontal and limbic brain regions.
The findings described above suggest that NAALADase inhibitors could be useful in treating glutamate abnormalities. In fact, the results of studies conducted by the inventors confirm that NAALADase inhibitors are effective in treating glutamate abnormalities, particularly stroke, Parkinson""s Disease, Amyotrophic Lateral Sclerosis (ALS) and spinal cord injury.
While a few NAALADase inhibitors have been identified, they have only been used in non-clinical research. Examples of such inhibitors include general metallopeptidase inhibitors such as o-phenanthroline, metal chelators such as EGTA and EDTA, and peptide analogs such as quisqualic acid and xcex2-NAAG. Accordingly, a need exists for new NAALADase inhibitors, as well as pharmaceutical compositions and methods using such new and known NAALADase inhibitors to treat glutamate abnormalities.
The present invention relates to a pharmaceutical composition comprising:
(i) an effective amount of a NAALADase inhibitor for treating a glutamate abnormality or effecting a neuronal activity in an animal; and
(ii) a pharmaceutically acceptable carrier.
The present invention further relates to a method of treating a glutamate abnormality in an animal, comprising administering an effective amount of a NAALADase inhibitor to said animal.
The present invention also relates to a method of effecting a neuronal activity in an animal, comprising administering an effective amount of a NAALADase inhibitor to said animal.